Field of the Invention
The invention relates to a housing having a housing section made of hard thermoplastic synthetic material for an electrical circuit, e.g. a motor vehicle locking system, to be protected from harmful substances, with at least one pressure member being accessible from outside the housing and with each pressure member serving to operate at least one electrical switch disposed or to be disposed inside the housing.
Although the invention was first developed for keys on a hand transmitter of a remote-controllable motor vehicle locking system, the new development of the keys in a motor vehicle on-board computer was also considered. The invention is also especially suitable for those two applications. However, it was finally found that the invention is also suitable for many other applications, especially for those in which it is important to achieve a reliable tightness against harmful substances or pollutants which can be easily and economically achieved, especially in mass production, for the keys of housings which contain circuits.
A main problem with the housing of such circuits is often the sensitivity of their electronic components to environmental effects, especially to moisture or water, but also to soiling. The tightness between the keys and the housing is critical, among other factors, because harmful substances can penetrate through gaps between the keys and the adjacent housing section.
Such keys generally contain a touch member or pressure member which serves to actuate a switch controlling the circuit, especially when the switch contains metal contacts. In principle, the invention may also relate to other kinds of switches which are to be operated through the touch member or pressure member. For the sake of simplicity, only "pressure members" will be referred to below, although the pressure necessary for operation may in principle be small enough for "touch members" to be referred to.
Many measures are known for avoiding any damaging environmental effects.
For example, the pressure members may be made of a soft flexible material, such as rubber, silicone or TPE, and then adhesively bonded at their edges or at peripheral, laterally upstanding collars or flanges to the hard housing in a watertight manner and are often additionally firmly clamped peripherally by webs, clips, tabs and the like in order to achieve the desired tightness. Sometimes the outer surface of the edge of the pressure member is additionally given a complicated notched or grooved shape and then the pressure member is pressed into the hole of the housing section in such a manner that the complicatedly shaped edge is pressed against the periphery of the housing section at the hole in order to achieve similar effects to labyrinth seals.
Sometimes, however, the pressure members are made of hard material, thus dispensing with the water-tightness between the key member and the housing. Instead of that, a space is formed under the pressure members and often also under the switches. The space is unprotected against the harmful substances and then in turn has a wall with a sealing diaphragm as sealing means for the electronics in the interior of the housing.
However, all of those known solutions are relatively complex and often unsatisfactory regarding their long-term reliability.
It is also known per se that soft thermoplastics which have been welded to hard thermoplastics or have been pressed onto one another in the liquid or doughy state readily adhere to one another after cooling, even though they are two different kinds of materials with different properties.